A Tracing Question (Alibre Atom) – Possibly Revealing One Huge Error!

[Nigel Graham 2Participant @nigelgraham2]

Examining Jason’s examples and turning to the Manual I found how to trace from a photograph, but must have missed something.

I wanted to ascertain dimensions and proportions from an image of the original. Given this for my steam-wagon engine, and it is prominent, I want it right to a reasonable degree, but have a sinking feeling I’ve been working under a gigantic scaling mistake for all the years since I started it.

I thought if I use both an Alibre tracing and test measurements by rule they should co-incide closely enough to verify my original measurements made too many years ago.

Once I worked out what I thought I was meant to do, I kept all scale controls to 1:1, and used mm to make the sums a bit simpler (so I thought). There is that calibration tool to refer the tracing to a known dimension but I could not see how to use it, or even if it works in Atom.

First I found if I saved the image, admittedly a scan of a photocopy of a photo, in the proper .jpg format but in an Alibre drawings folder, the CAD software itself could not find it. I copied the file to the desktop and that made Atom happy.

I put only the main outlines on the scan, and though the proportions all seem right the numbers are rhubarb!

I now had a set of 2D outline sketches to queer dimensions, on one page. I extruded them a couple of mm to create a single 2D Alibre drawing. I typed the derived dimensions into a spreadsheet, hoped conversion and scaling are correct, based on the (physical) model’s actual width, and added the inch equivalents for the model as text notes alongside each one.

Then found the miniature engine would be at least four inches too tall!

However, the drawing itself is strange.

Taking just the base width (8.25 inches / 208mm), of a part-made component:

Original photocopy of the archive photo: 84mm measured by rule. Pretty well 10mm : 1 inch.

Dimension on the sketch, given by the tracing: 499mm.

Alibre Drawing’s printed width (at 1:1 scale???): 100mm

Scale set by the software to fit the A4 sheet: 1:11

11 X 100 = 1100mm.

Dimension on that drawing: 499mm.

Alibre Drawing’s outline width: 100 mm.

 

What on Earth is happening there?

How can a line drawn in a sketch and on the print be indicated as so much longer than it actually is, and so far from the automatic page-scaling value ?

 

I have just repeated the drawing to see if I’d missed anything: No. I requested 1:1 scale on the first page, but the “Standard Views Creation” form says it has set the scale to 1:11. Sure enough, the elevation fits the page and repeats the 499mm dimension.

 

Essentially I’ve two problems.

1) Obviously I’ve done something wrong in driving Alibre Atom – but what, please?

 

The other is not a CAD-operating fault at all. All that tracing attempt reveals I totally cocked up my original interpretations of the archive photographs. Indeed, waving a rule over the photo bears out what Alibre and Excel show:

2) The whole ruddy project, fighting against a complete first-attempt failure, decades of house moves, struggle to learn CAD hoping it would help me design a working model from a few tatty old photos, lots of re-made parts, phases of clinical depression when I nearly scrapped it, a heck of a lot of money and time, is seriously wrong!

 

Effectively, this tracing has revealed I’ve built a 4″-scale chassis, wheels and superstructure around a boiler nearer 3″ scale size. So to make the engine so far drawn to fit as it should, means having significantly to change its external appearance, yet it is a very prominent part of the vehicle; part of the original Hindley wagon’s peculiar character.

Yet I am not confident the tracing is correct. It could not be very accurate but the errors are far larger than that. The print is larger than the scanned image, and the dimensions on both sketch and print match each other numerically but just do not make sense.

[JasonBModerator @jasonb]

When you put an image into Alibre to trace from there are two things to do with it.

1. Scale to size.

I do this first by starting a sketch on the same plane that I placed the image on and simply drawing a line to a known part often the flywheel diameter or in your case the base of (presumably) the engine and note it’s length which would be 499mm for your engine.

Now you say your actual piece of engine that is already cut is 8″ or 203 (not 208) so from that I can tell my image is Larger than the actual model. Quick bit of maths to work out that 203 divided by 499 = 0.401.

I now right click Trace image <1> down the left of the screen and select edit. From there I change the X & Y scale callibration from 1 to 0.401.

Here I measured the flywheel radius first of all and then adjusted the image so to suit a 125mm dia flywheel and then could just sketch a series of lines to get the relative size of other parts

 

2. Position

Not something that has to be done but I will then use the X & Y Offset to position the Alibre Axis lines somewhere convinient say with them crossing at the crankshaft axis or if looking at the front of your engine plat ethe vertical would be down themiddle. This makes it easier to take measuerments from those axis.

So with things the right size and in the right place start a sketch on the same plane that the image axis is on and every line or circle you draw will be to actual size so that any part placed over the sketch will fit. You can then just draw at 1:1 knowing the part will print at actual size assuming you have your printer correctly setup.

Here I have also moved the X & Y to cross on the crankshaft axis

There are two other things to watch out for, Alibre won’t correct perspective if the image is not square on and if your image has become stretched or squashed you may need to check the scale both horizontally and vertically and enter separate scaling correction for both.

 

 

[JasonBModerator @jasonb]

Dimension on the sketch, given by the tracing: 499mm.

Alibre Drawing’s printed width (at 1:1 scale???): 100mm

Scale set by the software to fit the A4 sheet: 1:11

11 X 100 = 1100mm.

Dimension on that drawing: 499mm.

Alibre Drawing’s outline width: 100 m

 

Even if you have not scaled the image correctly you are not doing something right with your printing. You should not have 499 as the dimension and then have to fudge things by printing out at a scale of approx 2:5 (203 : 499)

Alibre Drawing’s printed width (at 1:1 scale???)

You should also be able to check the scale that Alibre has selected. When you first select the part from your file and get the various views to choose alibre also displays a scale that will allow all the elevations to fit on your chosen paper size. Or you can click an elevation and select edit scale which will show what it is set at. I suspect Alibe has use 1:5 which is why your paper part is 100mm long yet you wrongly drew it at 499 from the trace.

But you can get it to print out at actual size by altering the scale to 203:499

Once again send the file with the trace and the drawing file to me or David.

[David JuppParticipant @davidjupp51506]

Nigel,

Atom3D has no idea what size the ‘real thing’ shown in the photo is – hence the calibration option when selecting a ‘tracing image’.  You have to tell Atom3D the actual size of something in the image is – typically be selecting 2 points in the image and entering the distance between them.   If the points used for calibration are not horizontal or vertical with each other, the image scale will be adjusted in both X & Y directions.

https://help.alibre.com/articles/#!alibre-help-v28/features-standard-features-tracing-image

 

2D Drawing scale – Atom3D will choose a view scale value to make all selected views fit on the chosen sheet size (I find it tends to go a bit smaller than I’d like).   You can alter the scale at will.

A dimension applied on the 2D drawing (or in the 3D model) will tell you what size Atom3D thinks the item is.

Send the files (including the photo) and information on actual size (or desired scale size).

I suspect that you have not calibrated the tracing image correctly – but I can only verify that if I have access to the files.

 

[David JuppParticipant @davidjupp51506]

Nigel – I appreciate that you don’t like video tutorials, but this one does show quite clearly how to calibrate a tracing image.

https://www.youtube.com/watch?v=v1Md2aCFN0w

[Nigel Graham 2Participant @nigelgraham2]

Thankyou.

I’m still vague what I did wrong apart from not calibrating the photo.

I did not “fudge” the printing scales but let Alibre calculate what would fit the paper from how it measured the photo.

 

I’ve just tried again with something much simpler, a Jeweller’s Anvil. I no longer have it, as I gave it to a friend whose hobbies include silver-smithing. So I can’t measure it but the rule gives a near-enough idea for this test.

I found how to use that calibration tool, but still ended up with strange results shown below, though at least this time I could produce a print that matches the length and height Alibre thought are right; both in physical image and the stated dimensions.

So tried again, typing into the calibration the length judged by eye from the rule,  but this time leaving the scale values as Alibre thinks.

I didn’t take it as far as a drawing but at least the tracing dimension, just the length of the anvil’s foot, now closely matched the judged length.

This was with the length calibrated but also the scale set to 1:1 –

As for the other problem, that of what seems a huge mistake in how I’d measured the original photo, I’ll just have to live with it and a potential glaring error in the engine’s appearance.

 

 

[JasonBModerator @jasonb]

You need to work out the ratio between what a line drawn in Alibre shows it’s length to be and the actual measurement, in this case what the rule shows.

I read the rule a 2 7/16″ and my import of your image the Alibre sketched line is 2.305″ so I need to slightly increase the image therefore 2.4375/2.305 say 1.06 so that is what you enter in teh scale boxes

Having now scaled the image if I go back and draw a line again this time instead of being 2.305 long it is 2.439 by eye and I could adjust it further by giving it an actual length.

Closed the sketch and extruded it a nominal 1″ about mid point

Produce a drawing for it, alibre defaulted to 1:1 scale and added a couple of dimensions Alibre giving the lengths to the lines I clicked

 

Then printed it out and put a rule against it, 2 7/16″

[Nigel Graham 2Participant @nigelgraham2]

I’ve just closed another attempt at the original engine scan. Although I managed to calibrate it, it produced so many invisble, untraceable so unrepairable “sketch errors” I had to abandon it.

The error table says it can help you find them… it might if could highlight where. It merely names their types.

I can only think this was because it was three separate rectangles instead of a single polygon or nested ones, but it seemed to accept more than that yesterday.

 

I’ll have to scale the photo manually. By sheer chance it is pretty well exactly 10mm of photocopy = 1 inch of physical steelwork; and square-on enough for no significant foreshortening and perspective.

(I don’t know where my proper film version has gone. The workshop gremlins occupy the house too.)

 

The whole project is coming dangerously close to the scrap-yard…… It’s barely progressed since this photo taken in June this year nearly gone:

[David JuppParticipant @davidjupp51506]

Nigel,

You have to select each listed error in the analysis table in order to see the location highlighted.

[Nigel Graham 2Participant @nigelgraham2]

I tried that David, but couldn’t make it work. It didn’t highlight anything.

I enlarged the joints hugely but the faults were still invisible even by slightly distorted black dots.

Deleted and restoring each line in turn found one stacked duplicate, which I removed: no difference.

I went round every junction with that Intersect tool: no difference.

There was a tiny rectangle off to one side, indicating the position of a shaft. I deleted that, thinking it might hold the fault – no difference.

Nothing worked.

[David JuppParticipant @davidjupp51506]

Nigel – I keep saying, but you refuse to take any notice, save the file and send it to me.

I can only guess at the problem if you post a general moan.  If I have the file I can determine whether the problem is ‘pilot error’ or an issue in the software.

[JasonBModerator @jasonb]

If you had 3 rectangles why not just use the rectangle tool to sketch 3 rectangles roughly and then pull each line into place. No risk of the ends not meeting as you seem to be getting with poorly placed lines.

You can have as many rectangles or polygons in one sketch as you like provided they are properly sketched and each is closed.

[David JuppParticipant @davidjupp51506]

Whilst you can have multiple rectangles (or other outlines) in a sketch, I’d suggest don’t go mad…

It’s much easier to diagnose and fix errors if the sketch is not too ‘busy’.  If worst comes to worst and you end up having to abandon (delete) a particular sketch, it’s less work to re-do if it is fairly simple.

[David JuppParticipant @davidjupp51506]

Nigel,

I suspect you are confusing ‘sheet scale’ and ‘view scale’ in Atom3D’s 2D drawing mode.

Sheet Scale is simply a number to display on the sheet to indicate your usual scale – it doesn’t actually set any view scale.  Though I understand why it is available, I suspect for many it is just confusing.

View Scale is the actual scale used to create views – Atom3D will initially choose a value to make sure all views fit on the sheet, but you can override this, or go back later and change it.  You can also add a scale legend to each view if desired.

[JasonBModerator @jasonb]

I’m also wondering what you are doing when sketching three rectangles to get into so many problems.

Alibre with start the 2nd line from where the first ended and so on then will snap the end of the 4th line back to the start of the first line so giving a closed sketch.

If you are drawing a line, then selecting the line tool again or clicking teh ESc key to draw the next and so on and don’t have some form of snap set then you are more likely to run into problems with lines not meeting or crossing over each other.

 

[David JuppParticipant @davidjupp51506]

Further to Jason’s post, the value set for snap threshold is important.  The ‘best’ value will depend to some extent on the size of parts you typically work with, and DPI of your monitor.

A value of zero will mean you have to be pixel perfect to get sketch figures to join to each other.  Too large a value and you may find you’ll get many unwanted snaps.

I’ve found that 3mm works well for me, that might be a good starting value – then adjust if needed.

 

[Nigel Graham 2Participant @nigelgraham2]

Jason –

I think I did use rectangles rather than trying to join lines, because the image outline is not very clear. It’s also of a slightly tapered, highy-radiused casting very slightly oblique to the camera.

The original was of a wagon still without its bodywork, and probably for the manufacturer’s purposes rather than the trade advertisements I’d already been trying to scale.

(Though even that’s not entirely reliable. The ads sometimes used photographs not those of the reviewed vehicles.)

When creating a polygon from separate lines I sometimes make them overlap then trim them back to each other, and that normally seems to work.

David –

I’ll look out for that snap setting. I didn’t realise it is adjustable. Alibre Atom hardly mentions it.

I’d’ taken “sheet scale” to be part of ensuring the image will fit the sheet, but still the numerical size of the drawing itself.

 

”””

I’m becoming so worn down by the whole thing. Even if I finish it and it works, it will not look right. I may as well try to complete the engine now underway and try and install it in the chassis as it’s meant to be, with no hope of fidelity to prototype. I had no idea just how far out of proportion the unit is until I revisited that photograph.

Below the scan of the relevant area of the photo, is the CAD assembly of the model engine so far – taking many evenings and frustrations to create. The finished engine will be 16″ high from sump floor to cylinder top, same height as the boiler, which protrudes just over 8″ above the chassis.

The scan shows the back of the engine, nearly but not quite vertical. The boiler top immediately beyond it is slightly below the engine top, but using the engine as I have partly made it so it matches this photo, will create a massive four-inch discrepancy on the miniature.

My measurements of the old photos had suggested the full-size boiler and engine tops were about two feet above the chassis. This scan, one or two photos showing the vehicle with its driver, and experimenting with a tape-measure while I sat on an ordinary chair, shows my boiler, the bunkers and perhaps crew seats are to the wrong heights.

To place the engine correctly, but as I’ve drawn and part-made it, sinks it to those little protruding covers, so all out of proportion. It also means the entire rear cover, with its little protrusions and large wing-nuts, would not be “quickly detachable” to quote the builder’s catalogue. The cross-member would be in the way.

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